Add docstrings and typing to db_engine_specs and sql_parse (#8058)

* Add typing to db_engine_specs

* Add more type annotations and docstrings

* Add docstrings and typing to sql_parse and db_engine_specs

* Refine select_star

* Fix execute and add more docstrings

* Revert kwargs change from execute

* Remove redundant or

* Align view and table getter schema types

* Fix return type of latest_partition

* Remove some typing from presto

* Improve docstring for __extract_from_token

superset/db_engine_specs/postgres.py

@@ -15,6 +15,11 @@
 # specific language governing permissions and limitations
 # under the License.
 # pylint: disable=C,R,W
+from datetime import datetime
+from typing import List, Optional, Tuple
+
+from sqlalchemy.dialects.postgresql.base import PGInspector
+
 from superset.db_engine_specs.base import BaseEngineSpec, LimitMethod
 
 
@@ -36,7 +41,7 @@ class PostgresBaseEngineSpec(BaseEngineSpec):
     }
 
     @classmethod
-    def fetch_data(cls, cursor, limit):
+    def fetch_data(cls, cursor, limit: int) -> List[Tuple]:
         if not cursor.description:
             return []
         if cls.limit_method == LimitMethod.FETCH_MANY:
@@ -44,11 +49,11 @@ class PostgresBaseEngineSpec(BaseEngineSpec):
         return cursor.fetchall()
 
     @classmethod
-    def epoch_to_dttm(cls):
+    def epoch_to_dttm(cls) -> str:
         return "(timestamp 'epoch' + {col} * interval '1 second')"
 
     @classmethod
-    def convert_dttm(cls, target_type, dttm):
+    def convert_dttm(cls, target_type: str, dttm: datetime) -> str:
         return "'{}'".format(dttm.strftime("%Y-%m-%d %H:%M:%S"))
 
 
@@ -58,7 +63,9 @@ class PostgresEngineSpec(PostgresBaseEngineSpec):
     try_remove_schema_from_table_name = False
 
     @classmethod
-    def get_table_names(cls, inspector, schema):
+    def get_table_names(
+        cls, inspector: PGInspector, schema: Optional[str]
+    ) -> List[str]:
         """Need to consider foreign tables for PostgreSQL"""
         tables = inspector.get_table_names(schema)
         tables.extend(inspector.get_foreign_table_names(schema))